1. Field of the Invention
The present invention pertains to lubrication systems for lubricating the bearings of bearing equipment items. More specifically, the present invention pertains to lubrication systems in which an oil mist is formed by combining air and oil and then distributed to the bearings to be lubricated.
2. Description of the Prior Art
For many years bearings have been lubricated by various means. In early lubrication systems, bearings were lubricated by "one shot" application of grease and/or oil to a grease or oil fitting with a grease gun or oil can. Although attempts were made to apply the grease or oil at needed periodic frequencies, it is obvious that at times too much oil and/or grease was used, and at other times, not enough oil and/or grease was provided for lubrication. For this reason, lubrication systems which apply the lubricant and at timed, periodic intervals or on a continuous basis, were developed.
U. S. Pat. No. 4,445,168 discloses a microcomputer controlled lubrication system which monitors and controls lubrication. In this system, individual "shots" of lubricant are periodically delivered based on either a time cycle or a machine stroke cycle. Other systems, such as the one disclosed in U.S. Pat. No. 4,527,661 utilize what is referred to in the industry as an "air - oil lubrication system" in which separate oil and air streams are brought to and combined by a mixing device, i.e. an atomizer, at a point immediately adjacent to the bearing being lubricated. However, such systems require two sets of piping (one for oil and one for air) and individual mixing devices at each point of lubrication.
In more recent years, oil mist lubrication systems have been developed to provide continuous, effective lubrication to anti-friction bearings of rotating equipment such as centrifugal pumps, electric motors, steam turbines, gear boxes, blowers, and fans. An oil mist lubrication system typically comprises an oil mist generator in which a compressed air stream in turbulent flow is combined with a liquid lubricant to create a fine mist of oil particles suspended in an air stream. These oil particles are typically one to five microns in diameter. The oil mist is transported through a piping system and delivered into the bearing housings of rotating equipment. The oil mist continuously lubricates the bearings of the equipment and maintains a slight positive pressure in the bearing housing to reduce contamination from outside sources.
When oil mist is generated, the oil is atomized into very fine particles so that the oil mist will remain stable and can be transferred relatively long distances with minimum wetting out on the walls of the pipe in which it is being conveyed. These fine particles, referred to as "dry mist", must be converted into larger particles, referred to as "wet mist", in order to wet out on the metal surfaces of the equipment bearings being lubricated. This is accomplished by passing the dry mist through a specially designed restriction orifice known as a "reclassifier". The reclassifier induces turbulence in the stream to combine small particles into larger ones before the mist (wet mist) enters the equipment bearing housing. These reclassifiers serve the additional purpose of metering the amount of lubricant to each bearing to avoid over or under lubrication. Selection of the correct reclassifier for each application point in the system is based upon an understanding of the exact bearing configuration for each piece of equipment to be lubricated.
An especially advanced oil mist lubricating system is disclosed in U.S. Pat. No. 5,125,480. It includes an air supply, the inlet of which is connected to a source of pressurized air; an oil supply; an oil mist generator connected to the air supply and the oil supply and by which air and oil therefrom are combined in an oil mist for distribution; and microprocessor control means for controlling and monitoring the operating conditions of the system. Such a system provides for continuous lubrication of the bearings of rotating equipment with greatly improved monitoring and control characteristics. Operating variables of the system are maintained within desired limits and oil consumption and oil mist density are accurately controlled, reducing oil consumption and environmental pollution.
Even though recent oil mist systems, such as the one disclosed in U.S. Pat. No. 5,125,480, offer much more effective and efficient lubrication, such systems, unfairly in many cases, are criticized for environmental pollution. It is true that some of the oil mist particles, particularly the smallest ones, do not wet out on the metal surface of the equipment being lubricated. They may pass through bearing housings and vent to the atmosphere. In addition, although much less excess oil may accumulate near the lubricated bearings in an oil mist lubrication system, a certain amount of excess oil will accumulate. In the past, collection vessels have been provided, whether in oil mist systems or in the older conventional lubricating systems, to collect the excess oil for periodic recovery and/or reuse. Many times, however, the excess oil is collected in a open container susceptible to contamination by rain water or other substances. In many obsolete systems, such oil was simply drained to sewers.